Combine all sauce ingredients except butter and mustard in a large pot and bring to a simmer. Simmer on low for 6 hours.

Strain through a fine mesh sieve into another pot. Return liquid to med-med high heat and begin reducing. You don’t want it to be at a raging boil. Keep it just above a simmer and keep a pretty constant eye on it. It will probably take at least an hour to reduce to the proper consistency, most likely longer. Do the spoon test to check for doneness: Stick a spoon in the sauce and make a line through it with your finger on the back of the spoon. If the line holds, you’ve reached the correct consistency. If the line doesn’t hold, it needs to reduce further. You should have about 1.5 cups of sauce when it has reduced fully.

When sauce reaches the desired consistency, remove from heat and whisk in the butter and mustard.

Check the sauce for seasoning. Add salt if necessary. If it is too salty, balance it by adding more butter and more mustard. Keep warm or refrigerate if not using immediately.

Pre-heat the oven to 400°F. Season the meat generously with salt and pepper. Place on a sheet pan equipped with rack insert. Allow to sit at room temp for 30 minutes prior to roasting.

Roast the meat to an internal temp of 135 degrees. (In Spain, Iberico pork is typically cooked to medium rare.) Allow to rest for 10 minutes prior to slicing. Serve with warm sauce and enjoy!